Tetrahydrohyperforin Inhibits the Proteolytic Processing of Amyloid Precursor Protein and Enhances Its Degradation by Atg5-Dependent Autophagy

Abstract

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid-β (Aβ) peptide. We have previously shown that the compound tetrahydrohyperforin (IDN5706) prevents accumulation of Aβ species in an in vivo model of AD, however the mechanism that explains this reduction is not well understood. We show herein that IDN5706 decreases the levels of ER degradation enhancer, mannosidase alpha-like 1 (EDEM1), a key chaperone related to endoplasmic-reticulum-associated degradation (ERAD). Moreover, we observed that low levels of EDEM1 correlated with a strong activation of autophagy, suggesting a crosstalk between these two pathways. We observed that IDN5706 perturbs the glycosylation and proteolytic processing of the amyloid precursor protein (APP), resulting in the accumulation of immature APP (iAPP) in the endoplasmic reticulum. To investigate the contribution of autophagy, we tested the effect of IDN5706 in Atg5-depleted cells. We found that depletion of Atg5 enhanced the accumulation of iAPP in response to IDN5706 by slowing down its degradation. Our findings reveal that IDN5706 promotes degradation of iAPP via the activation of Atg5-dependent autophagy, shedding light on the mechanism that may contribute to the reduction of Aβ production in vivo.

Autophagosomes cooperate in the degradation of intracellular C‐terminal fragments of the amyloid precursor protein via the MVB/lysosomal pathway

“…In addition to the evidence showing that APP is sorted to the endolysosomal pathway for delivery to lysosomes (25, 26, 28, 33), other findings indicate that the cellular levels of both APP and C99 are also regulated by autophagy (31, 32, 34). However, the contribution of both pathways in the total clearance of these amyloidogenic membrane proteins remains unknown.…”

“…Interestingly, TSG101 depletion results in accumulation of APP/CTFs in an endolysosomal compartment that appears to contain proteins of both early endosomes and MVBs/lysosomes, such as EEA1 and LAMP1, respectively (26, 28, present study), emphasizing the need of normal maturation of early endosomes into MVBs to avoid accumulation of amyloidogenic proteins. In addition to the evidence showing that APP is sorted to the endolysosomal pathway for delivery to lysosomes (25,26,28,33), other findings indicate that the cellular levels of both APP and C99 are also regulated by autophagy (31,32,34). However, the contribution of both pathways in the total clearance of these amyloidogenic membrane proteins remains unknown.…”

“…After the final wash, coverslips were mounted onto glass slides with Fluoromount‐G (SouthernBiotech, Birmingham, AL, USA). Images of fixed cells were acquired with an AxioObserver.D1 microscope equipped with a PlanApo ×63 oil‐immersion objective (NA 1.4) and an AxioCam MRm digital camera (Carl Zeiss GmbH, Jena, Germany), using similar settings described previously (34), or with an Olympus FluoView FV1000 scanning unit fitted on an inverted Olympus IX81 microscope equipped with a PlanApo ×60 oil‐immersion objective (NA 1.4; Olympus, Tokyo, Japan), using similar settings as described previously (35). Alternatively, images of fixed cells were acquired by a DeltaVision OMX system (GE Healthcare Life Sciences, Issaquah, WA, USA) for superresolution by structured illumination microscopy (SIM), using similar settings as described previously (36, 37).…”

Inhibition of Wnt signaling induces amyloidogenic processing of amyloid precursor protein and the production and aggregation of Amyloid‐β (Aβ)42 peptides

“…; Cavieres et al . ). For these assays, 100 μL of conditioned medium was collected to measure the Aβ 40 and Aβ 42 levels according to the manufacturer's instructions.…”

“…To determine the concentration of Ab peptides, sandwich enzymelinked immunosorbent assays specific for Ab 40 and Ab 42 were used as previously described (EZBRAIN40, EZBRAIN42; EMD Millipore Corporation, Billerica, MA, USA) (Mufson et al 2012;Cavieres et al 2015). For these assays, 100 lL of conditioned medium was collected to measure the Ab 40 and Ab 42 levels according to the manufacturer's instructions.…”